The invention relates to a measuring technique of a wedge tightness which is used to fix a stator coil in a stator of a generator or the like.
A generator is constructed by a rotor and a stator and converts a change in magnetic field generated by a rotation of the rotor into an electric energy by the stator. The stator has such a structure that a coil is inserted into a slot of a core laminated with a silicon steel plate and is fixed with a pressure by an insulative member. As a pressure fixing method, the stator has such a structure that a ripple spring and a wedge serving as a plate-shaped member are overlaid over the coil and has such a structure that while compressing the ripple spring, it is pressed by the wedge, thereby fixing a coil conductor. In the generator having such a structure, it is necessary to maintain and manage the coil so as to be in a predetermined pressure fixing state. In the generator having such a coil fixing structure, after the elapse of predetermined years and months of use, the fixing state of the wedge is inspected and if there is looseness, an exchange and a maintenance of the ripple spring and the wedge are performed in order to recover a pressing force. Hitherto, an inspection and a discrimination of the coil fixing state have been performed by a person in dependence on such a sensory test that he applies a tap to the wedge by using a hammer for inspection and discriminates the coil fixing state on the basis of a tone and a vibration which are generated at this time. As a trial for realizing such a sensory test by an apparatus, there is a technique disclosed in JP-A-2000-131196. According to such a technique, a peak value in each frequency band of the tone which is generated by the hammer tap to the wedge is obtained and is compared with a preset reference value, thereby discriminating a looseness state.